INTRODUCTION

Back then in the stone ages, information were disseminated either on foot or via beasts such as horses or camels. The rate at which information were disseminated was very slow. A person on foot would take days or even months to deliver a piece of information across a distance.

With the use of beasts, dissemination of information was a bit faster and became more and more faster like the speed of lightening with our transition into twenty first century, an era of explored science and technology. Things have really become easier and can be done faster.

You could be sitting in your room and dial a number on your phone and be instantly connected with a friend millions of miles away. The messages we type and send the conversations we make over our cell phones are all conveyed via electromagnetic waves or em wave as others may call it.

There are different types of EM (Electromagnetic waves) wave but we will strictly be focusing on radio wave; what it is? how it is propagated? how it can be detected? and of course how to make a simple radio receiver? In order to understand it better, let’s see some few things first.

EM WAVE

Electromagnetic wave or EM wave is a form electromagnetic radiation that results from the discharge of electricity or even lightening. Any discharge of electricity can result to EM wave with wavelength close to that of radio wave.

Electromagnetic radiation posses wave properties, i.e, EM wave can be propagated, diffracted, refracted etc. EM wave can be interfered i.e it undergoes interference when an EM wave with the same or close range frequency cross its path. EM wave ranges from radio wave which has low frequency with long wavelength to gamma ray that has the highest frequency and shortest wavelength hence gamma ray has the highest energy.

RADIO WAVE

Radio wave is a form of electromagnetic radiation. It has low frequency which approximately ranges from 150kHz to 100MHz.

OSCILLATORS

To better understand how data is transmitted via radios, it is necessary that we talk about an oscillator. An Oscillator is of two types; there is the mechanical oscillator and an electrical oscillator but we will focus on electrical oscillator only. An electrical oscillator or vibrator can be made by connecting a capacitor to a coil.

The system is made to oscillate by providing the capacitor with an electric charge. The energy is stored alternately between the plates of the capacitor and in the coil in form of magnetic field. Energy is transferred from the coil to the capacitor and from the capacitor to the coil, and back again as the system oscillates.

The flow of energy involves the flow of electric current. The flow of electric current causes some of the energy of the system to be transformed to internal energy in the capacitor, coil and the connecting wires.

RADIO TRANSMITTER

When there is a discharge of electricity, electromagnetic radiation of radio frequency is produced. Crackle sound is produced on a radio set when is lightening due to interference between the radio wave produced by the lightening and that transmitted by a nearby station. A small spark around the home may produce a noise on a radio set.

A spark is produced by turning a switch on and off especially those carrying heavy current. Sparks produced by thermostat switches in cookers and refrigerator, spark at the contact of electric bell etc are all liable to produce an EM wave that is detected by a radio set. Early radio transmitters operated on the principle of spark production. Modern transmitters operate differently. They consist of different sections;

Oscillator: it is made up of a capacitor and a coil. The capacitor and the coil are chosen so that the circuit oscillates at frequency of several kHz or MHz. If the circuit is connected to an aerial or antenna, an oscillating electric field is created in the wire.

Feedback amplifier: Due to energy loss, the oscillator cannot supply the aerial with energy unless it is supplied with energy to make up for its loss. Energy supplied to the oscillator Must be in resonance with the oscillator. To achieve this, we take a small fraction of the oscillating current from the oscillator while the rest goes to the antenna. The minute fraction of the current we take is fed into an amplifier. The output of the amplifier is a large oscillating current. It has the frequency as the oscillator. The large electric current is then fed into the oscillator so that it supplies the energy it needs to make the circuit oscillate continuously.

MODULATOR

A radio transmitter could produce only a continuous strain of radio wave of constant frequency and amplitude if the transmitter contains only an oscillator and a feedback amplifier. The more modulator modulates the frequency (FM).

In a radio transmitter, audio frequency e.m.f is fed into the modulator. The carrier wave is fed into the modulator also. The modulator then modulates the amplitude of the carrier wave to follow the wave form of the audio frequency e.m.f. The amplitude modulated carrier wave is then fed to the antenna.

RADIO WAVE DETECTION

For some reasons, radio waves are reflected by a parabolic reflector that is aimed at a receiving station many miles away. Reflectors are used for transmission to and from telecommunication satellites and for microwave radio links used in telecommunication system.

When the electromagnetic radiation reaches a metallic object, it produces minute electric current in it. The aerial is used to catch the radio waves.The aerial or antenna carries currents produced by all the nearby transmissions that reach it. When we try to listen to it, we would not hear clear distinct sound because there are many of the sound waves received by the radio receiver.

To hear a distinct sound transmitted by one of the transmitting stations, a radio receiver is used to tune to a particular channel. The receiver consists of;

Tuner: it is primarily made up of a capacitor-coil circuit. The frequency of the oscillation is varied by varying the capacitance of the capacitor so that it has the same frequency as that of the transmitting station we receive.

Rectifier: Nothing will be heard when an earphone is connected across a capacitor though the current is oscillating. It is so because the frequency (150kHz or more) is above the frequency our ear can detect. The rectifier helps us to hear the sounds clear.

Amplifier: The amplifier will amplify the current so that the sound can be heard even in a loud speaker.

HOW TO CONSTRUCT A SIMPLE RADIO RECEIVER

To construct a simple radio receiver follow the steps given below:

Connect your antenna, diode, earthing cable and your tuner in series with the variable capacitor connected in parallel across the coil. The antenna can be any insulated wire of length 25m long.

Bury a strip of metal in the soil and connect the earth wire to it. If the soil in which you are to bury the metal strip is dry, wet it by applying water to it.

Make the coil by winding about 80 turns of insulated wire on a ferrite rod which improves the properties of the coil.

Use a variable capacitor with few capacitance say hundred Pico farads (pf). If you can’t find such, use a fixed capacitor that ranges from 10pF to 470pF.

The diode to be used should be OA91. It is a germanium diode. Other germanium diode can be also used.

If you get no result, try 40 turns of coil and if still no result it’s probably because your nearby transmitting station is not powerful enough for such circuit to receive.
Simple Circuit of a Radio Receiver with One Stage of Amplification

You think your nearby transmitting station is powerful but still no result? Relax! In that case you need to introduce an amplifier into the circuit. Make your connection as in the diagram. That is a simple radio for you. A radio signal has the least energy and so cannot convey large data at an instance. It’s suitable for local/close range transmission because most of the things transmitted over the radio are audio which the radio wave can convey without delay.

Why radio waves is chosen for remote/close range Transmission ?

You might have wondered why the other em waves are Not used for close range transmission and cannot be used for transmitting the signals to remote areas. Well, Radio waves do not provide heating effect unlike microwave.

Radio waves with lower frequency are diffracted thereby making it possible for people behind hills to receive the signals. Unlike Other em wave, radio wave receivers need not to be in front of a Transmitter to Receive the signals.

For low Frequency radio, their ability to be diffracted makes it possible for signals to be received behind hills. Repeater stations are used to improve the quality of the signals. The other em waves are not easily diffracted.